Electrolytic fused salt cleaning bath



1956 H. G. WEBSTER ET AL I 2,732,339

ELECTROLYTIC FUSED SALT CLEANING BATH Filed Aug. 2, 1951 2 Sheets-Sheet 2 as 2e a 5 ,0

Figfiffl I u. jz 23 36 L FjE] 4- 24 2 ,r 27 L g 27 Egyfi INVENTOR3 BYK/ Amy fm 66 United States Patent ELECTROLYTIC FUSED SALT CLEANING BATH Hugh Graham Webster and Ray W. Thomas, Detroit, Mich., assignors to I. H. Shoemaker, Detroit, Mich.

Application August 2, 1951, Serial No. 239,934

2 Claims. (Cl. 204-243) This application relates to electrolytic liquid bath con structions and aims to provide new and useful improvements in such constructions.

A prior Patent No. 2,515,148 of July 11, 1950, describes an electrolytic bath of the molten alkali salt type for cleaning work pieces immersed in such bath, the bath itself being a molten, fused mixture of sodium hydroxide, sodium chloride, and sodium aluminate, with or without, as desired, a modicum of sodium fluoride. In some uses of that bath, the work is electrically connected as a cathode; in others, alternately as cathode and anode cycli-. cally. This application specifically relates to construction features particularly designed for such baths.

For an understanding of such features, reference will be had to the appended drawings and to the following specification. 1

In such drawings:

Fig. 1 is a diagrammatic top plan view of an electrolytic bath.

Fig. 2 is a diagrammatic longitudinal section view.

Fig. 3 is a diagrammatic end section view.

Fig. 4 is a fragmentary diagrammatic top plan view.

Fig. 5 is an enlarged fragmentary diagrammatic end view.

An electrolytic bath construction includes a double walled pot or tub having an upper wall or edges 11 and having means, not shown, for heating the contents of the inner wall or tub 12. Such contents may be any desired electrolytic composition and, for purposes of illustration, such contents will be the molten fused mixture, as above described, with such mixture filling the tub 12 to the level shown at 14.

A. Work mounting For removably supporting and for making temporary electrical contact with the work immersed in the bath, means such as will now be described are provided. Such means includes a work holder in the form of a mesh or perforate basket or tray 20 having at its ends yokes 21 connected at the top by a bail 22 provided with handling hooks 23 and outwardly extending mounting and contact lugs 24.

Mounted in any suitable manner above the tub as, for example, on insulating blocks 25, are rails or bus bars .26 to which are bolted at points near the ends of the tub 27 are below the level 14 of the bath so that the lugs 24' are immersed in the bath when there is current flow 2,732,339 Patented Jan. 2.4-, 1956 2 between the bus bars and the work on the one hand, and the tub 12 on the other.

In a preferred form the lugs 24, as shown best in Fig. 5, are of a cross-section complementing the intersection or V joints of the straps 27 whereby these lugs engage the strap with surface-to-surface contact with as little air gap as possible between the lugs 24 and the straps 27.

The straps 27 are intended to be expendable and for this reason, though considered as permanently mounted, the fact is that they are secured to the permanently mounted bus bars 26 by bolts 28 which when tightened create low resistance joints at 28 between the straps 27 and the bus bars 26, but which may be removed to permit replacement of eroded straps 27 by fresh ones to restore the satisfactory functioning of the bus bars 26 for supporting the Work and the work holder 20.

It has been found that a remarkable reduction in erosion and a remarkable improvement in the functioning of the bath has been effected by the disposition of the points of removable attachment and of temporary electrical contact between the work holder 20 and the work holder support 27 below the level of and constantly immersed in the bath 12.

See

B. Sacrificial plate Instead of utilizing the pot or tub 12 as one of the electrodes of the bath, particularly Where the bath is of the direct current type with the work as the cathode and the tub 12 as the anode, improvement is efiected by the use of a sacrificial plate to which the anodic current supply is connected, such plate serving as the anode. The drawings show such a construction comprising one or more plates 30 arranged to line the tub 12 and having outwardly extending lugs 31 resting on blocks 32 mounted on the upper wall 11 of the pot. Blocks 32 are of insulating material and, hence, insulate the pot from these anodes 30, connected in any suitable manner to the anodic supply.

The plates 30 are immersed in the bath. For purposes of economy and for improving their functioning, it is preferred to make the plates 30 of grid or mesh form.

Grids must have no horizontal surfaces, upon which sludge can settle. However, they have been used in plate form or strip form and found satisfactory.

It has been found desirable to space the grids somewhat remote from the straps or VS 27, the distances being varied as found best. It is observed that if the grids and Vs are too close together in a molten salt bath, current will flow directly from the straps to the grids, rather than from the straps through the Work pieces in the basket to the grids, due to the fact that the salt bath is a good conductor of electricity. A flow of current, not through the work pieces, impairs the efiiciency of the bath.

It has also been found desirable to construct each grid of uniform cross section to avoid concentration of cur rent flow on heavier or larger portions of grids of nonuniform cross section. For similar reasons all grids in a bath should preferably be as nearly identical as possible and of nearly identical positioning with respect to the basket and work pieces.

it has also been found desirable to form the grids with as little horizontal sludge deposit surfaces as possible, to avoid the deposit of sludge on the grids and thus to avoid short circuiting of current from basket to grid sludge deposits.

Long use of the electrolytic baths has been found to cause electrolytic erosion of the tubs 12, particularly where these are connected as anodes. Replacement of eroded tubs 12 is a very expensive and delaying matter. Great economies are elfected by the use of the sacrificial plates 30 as the anodes for electrolytic erosion will be on these plates which are inexpensive and whichmay easily be replaced.

One or more plates 30 maybe used, as desired. If several are used, they may be of the form shown, and they may be interconnected electrically, by straps or other means, or separately connectedto the anodic supply, all as desired. However, it has been found that when the sacrificial plates of grid form are arranged in loop form, as shown in Figs. 1 and 4, there has resulted a greater degree of uniformity of electrolytic bath action on the work on holder 20.

Though the loop form is preferred, the single plate form has also been found satisfactory and has the advantage that it is much cheaper to fabricate and much more easy to remove the install.

Where the sacrificial plate, particularly of grid or mesh form, instead of the pot, is utilized as the anodic electrode, it functions as a heating plate to add heat to the bath. When the pot itself is used as an electrode, the heat dissipation from it destroys the effect of the pot as a heater.

The sacrificial plate immersed in the bath keeps itself clean and does not scale and has a tendency to add heat to the bath.

Particularly Where the bath is of the reversing current type where the work is successively cathode and anode, improvement has been observed in arranging that the sacrificial plate 30 and the pot 12 be electrically interconnected so that the sacrificial plate and the pot together form the electrode, with the sacrificial plate functioning as an erodable sacrificial and removable liner for thetub 12.

Wherev the sacrificial plate is utilized with reversing current, i. e., where the work is alternately cathodic and anodic, it has been found that the end of the pot is subject to a greater amount of electrolytic erosion and, hence, the sacrificial plates, even if not used on the sides of the pot, should at least be used on the ends of the pot adjacent the ends 21, 24 of the work holder or basket.

Now having described the bath constructions and improvements herein disclosed, reference should be had to the claims which follow.

We claim:

1. An electrolytic fused salt cleaning bath for cleaning a metal work piece suspended in the liquid of said bath by passing electric current therethrough while maintainingthe work piecefor at leastabout one half ofthe electrolytic treatment periodas a cathode, comprising an open top container forming a cell, two bus bars mounted substantially parallel along opposite upper edges of said container, a pair of V-shaped metallic stirrup members disposed a substantial distance from each other having each of their arms removably but firmly fastened to an opposite bus bar in current conductive support with the crotches of the said V members depending a substantial distance downwardinto the container as supporting members for objects positionable below the upper surface level of bath liquidin saidcontainerya basket of foraminous metal comprising a work holder within which the work pieces may be disposed, said basket having a pair of horizontal supporting lugs each laterally extending from an opposite end thereof, each positioned to be engagetl within a depending crotch of one of the V-shaped stirrups for gravitational support and temporary electroconductive contact therewith, whereby the foraminous basket is supported through said lugs between the pair of. V-shaped stirrups gravitationally without further fastening while beingdisposed completely immersed Within the liquid of said bath.

2. The apparatus asdefined in claim 1 wherein each of said lugs have at least the lower sides angularly bevelled to complement the sloping sides of the said V=shaped stirrups to form a substantial surface area for enhanced electroconductive contact with said V-shaped members.

References Cited in the file of this patent UNITED STATES PATENTS 803,544 Betts Nov. 7, 1905 1,251,568 Potthoff Jan. 1, 1918 1,267,653 Gillis May 28, 1918 1,376,052 Taylor Apr. 26, 1921 1,734,909 Jones Nov. 5, 1929 2,372,296 Saas Mar. 27, 1945 2,398,059 Turner Apr. 9, 1946 2,546,920 Cupps Mar. 27, 1951 FOREIGN PATENTS 342,477 Great Britain Feb. 5, 1931 21,233 Great Britain of 1898 10,102 Great Britain of 1902 

1. AN ELECTROLYTIC FUSED SALT CLEANING BATH FOR CLEANING A METAL WORK PIECE SUSPENDED IN THE LIQUID OF SAID BATH BY PASSING ELECTRIC CURRENT THERETHROUGH WHILE MAINTAINING THE WORK PIECE FOR AT LEAST ABOUT ONE HALF OF THE ELECTROLYTIC TREATMENT PERIOD AS A CATHODE, COMPRISING AN OPEN TOP CONTAINER FORMING A CELL, TWO BUS BARS MOUNTED SUBSTANTIALLY PARALLEL ALONG OPPOSITE UPPER EDGES OF SAID CONTAINER, A PAIR OF V-SHAPED METALLIC STIRRUP MEMBERS DISPOSED A SUBSTANTIAL DISTANCE FROM EACH OTHER HAVING EACH OF THEIR ARMS REMOVABLY BUT FIRMLY FASTENED TO AN OPPOSITE BUS BAR IN CURRENT CONDUCTIVE SUPPORT WITH THE CROTCHES OF THE SAID V MEMBERS DEPENDING A SUBSTANTIAL DISTANCE DOWNWARD INTO THE CONTAINER AS SUPPORTING MEMBERS FOR OBJECTS POSITIONABLE BELOW THE UPPER SURFACE LEVEL OF BATH LIQUID IN SAID CONTAINER, A BASKET OF FORAMINOUS METAL COMPRISING A WORK HOLDER WITHIN WHICH THE WORK PIECES MAY BE DISPOSED, SAID BASKET HAVING A PAIR OF HORIZONTAL SUPPORTING LUGS EACH LATERALLY EXTENDING FROM AN OPPOSITE END THEREOF, EACH POSITIONED TO BE ENGAGED WITHIN A DEPENDING CROTCH OF ONE OF THE V-SHAPED STIRRUPS FOR GRAVITATIONAL SUPPORT AND TEMPORARY ELECTROCONDUCTIVE CONTACT THEREWITH, WHEREBY THE FORAMINUOUS BASKET IS SUPPORTED THROUGH SAID LUGS BETWEEN THE PAIR OF V-SHAPED STIRRUPS GRAVITATIONALLY WITHOUT FURTHER FASTENING WHILE BEING DISPOSED COMPLETELY IMMERSED WITHIN THE LIQUID OF SAID BATH. 